A charge retaining means known as a"Swiss"groove formation, for retaining a cylindrical charge inside a barrel chamber of a cannon, comprises a semi- circular off-centre cutaway portion in the operatively lower wall of the barrel chamber. In use, a projectile is rammed into the chamber of the barrel.

Thereafter the charge is inserted into the chamber past the"Swiss"groove formation and released. The charge slides backwardly into the"Swiss"groove formation, with a lower end of the charge being retained by a lower end of the "Swiss"groove formation.

A first disadvantage of the"Swiss"groove formation is that the formation fills up with dirt and grime, making it ineffective and dangerous as the formation no longer retains the charge when filled up, so that the charge falls out of the barrel.

A second disadvantage is that it is relatively difficult and tedious to clean the formation regularly.

A third disadvantage is that the groove changes the chamber volume of the barrel chamber, which not only affects the operation of the cannon, but also changes the specifications of the barrel to parameters falling outside the Joint Ballistic Memorandum of Understanding.

A fourth disadvantage of the"Swiss"groove formation is that it is relatively difficult to manufacture, because it has to be cut into the chamber wall using a relatively large lathe. As the groove formation is disposed off-centre, the lathe bearings are subjected to extreme and severe loads by the unbalanced weight of the barrel when the barrel is being rotated on the lathe, causing unnecessary wear and tear of the lathe.

Another known charge retaining means comprises a retaining device and a resiliently flexible annular flange formation extending and flaring outwardly from a lower end of the charge. The flange formation deforms inwardly and frictionally engages the inside of the barrel when the charge is inserted, thus retaining the charge in position.

A disadvantage of a retaining device of this type is that the annular flange formation tends to interfere with the interchageability of different charge types,

owing to the differences in configuration of respective ammunition handling systems.

OBJECT OF THE INVENTION It is therefore an object of the present invention to provide a charge retaining mechanism, a gun and a barrel for a gun, both provided with such a mechanism with which the aforesaid disadvantages can be overcome or at least minimised.

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a charge retaining mechanism for retaining a charge inside a chamber of a barrel of a gun comprising a charge retaining member which extends into the chamber of the barrel and which is movable between a charge passing position and a charge retaining position.

The charge retaining member may be biased towards the charge retaining position.

The charge retaining mechanism may include biasing means for biasing the charge retaining member towards the charge retaining position.

The biasing means may be in the form of a coil spring.

The charge retaining mechanism may further include a groove formation in the inner surface of the barrel chamber and which extends at least partially around the inner circumference of the barrel. The coil spring may be located inside the groove formation.

Opposite ends of the groove formation may progressively cut deeper into the inside surface of the barrel chamber towards the full depth of the groove formation until a constant depth is reached.

The groove formation may be circular in cross-section. Furthermore, a slit of the groove formation may be relatively narrower than the diameter thereof, the arrangement being such that the groove formation is adapted such that the coil spring is located inside the groove formation by feeding the coil spring into the groove formation from one end. This configuration of the groove may therefore be referred to as a choked groove.

The charge retaining member may comprise a protrusion extending from the coil spring into the chamber of the barrel, through the slit of the groove formation.

The charge retaining mechanism may further include limiting means for limiting movement of the charge retaining member past the charge retaining position.

The limiting means may be provided by a side wall of the groove formation, with a portion of a side wall opposite to the limiting means, complementary to the protrusion, being removed to allow the protrusion to move to the charge passing position.

The charge retaining member is a first member and the charge retaining mechanism may include two sets of further members extending from the same coil spring and spaced from the first member, the arrangement being such that a central retaining member and two sets of end retaining members are provided.

Each set of end retaining members may include three adjacent retaining members.

The arrangement may further be such that the winding direction of the portions of the coil spring between the sets of end retaining members and the end of the coil spring extends in a first direction and the winding direction of the portions of the coil spring between each set of end retaining members and the central retaining member extends in an opposite direction.

The winding direction of the portions of the coil spring between adjacent retaining members of each set may be in the same direction, the arrangement

being such that the adjacent retaining members of each set are biased in the same direction.

According to a second aspect of the invention there is provided a barrel for a gun including a charge retaining mechanism according to the first aspect of the invention.

According to a third aspect of the invention there is provided a gun including a charge retaining mechanism according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described further by way of a non-limiting example with reference to the accompanying drawings wherein: figure 1 is a cross sectional view along line B-B1 in figure 2 of a barrel chamber of a gun provided with a charge retaining mechanism according to a preferred embodiment of the invention; figure 2 is a longitudinal sectional view along line A-A'in figure 1; figure 3 is a sectional view along line C-C'in figure 1, with the charge retaining mechanism in a charge passing position; and

figure 4 is the same view as that of figure 3, with the charge retaining member in a charge retaining position.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring to the drawings, a mechanism according to a first preferred embodiment of the invention, for retaining a charge 12 inside the chamber 14 of a barrel 16 of a gun (not shown), is generally designated by reference numeral 10.

The charge retaining mechanism 10 comprises charge retaining members including a central retaining member 18.1 and two sets of end retaining members 18.2, extending from a biasing means in the form of an elongate coil spring 20, into the chamber 14 of the barrel 16.

Each set of end retaining members 18.2 consist of three adjacent retaining members 18.2. 1.

The coil spring 20 is located in an elongate groove formation 22 cut into the inner surface of the barrel 16 and extending partially about the inner circumference of the barrel 16. The arrangement is such that the members 18.1 and 18.2 extend through an opening or slit 24 of the groove formation 22 into the chamber 14.

The groove formation 22 is a so-called choked groove and is circular in cross- section, with the opening or slit 24 being relatively narrower than the diameter of the groove formation 22. Opposite ends of the groove formation 22 are progressively cut deeper into the inside surface of the barrel 16 towards the full depth of the groove formation 22 until a constant depth is reached. The coil spring 20 is disposed inside the groove formation 22 by feeding the coil spring 20 into the groove formation 22 from one end.

The charge retaining members 18.1 and 18.2 are movable relative to the charge, between a charge passing position (shown in figure 3) and a charge retaining position (shown in figure 4).

The charge retaining mechanism 10 further includes a limiting means 26.1 and 26.2 for limiting the movement of the charge retaining members 18.1 and 18.2 past the charge retaining position. The limiting means is provided by a side wall 26.1 of the groove formation 22. A portion of an opposite side wall 26.2, complementary to the protrusion, is removed to allow the charge retaining members 18.1 and 18.2 to move to the charge passing position.

The retaining members 18.1 and 18.2 are biased in the direction of the charge retaining position by means of the coil spring 20. The direction of the windings of the coil spring 20 between the end of the coil spring 20 and the sets of end retaining members 18.2 is different to the direction of the windings of the coil

spring 20 between the sets of end retaining members 18.2 and the central retaining member 18.1.

The winding direction of the portions of the coil spring 20 between adjacent retaining members 18.2. 1 of each set of end retaining members 18.2 is in the same direction, the arrangement being such that the adjacent retaining members 18.2. 1 of each set of end retaining members 18.2 are biased in the same direction.

In use, a projectile (not shown) is first rammed into the chamber 14 of the barrel 16. Thereafter, the charge 12 is inserted (shown by arrow F in figure 3) into the chamber 14, with the charge 12 forcing the charge retaining members 18.1 and 18.2 against the bias of the coil spring 20 to the charge passing position. After the charge 12 has passed the members 18.1 and 18.2, the coil spring 20 returns the members 18.1 and 18.2 to the charge retaining position. The charge then slides backwardly (shown by arrow G in figure 4) against the charge retaining members 18.1 and 18.2. The charge 12 is thus retained inside the barrel 16.

The applicant foresees that the charge retaining mechanism 10 can easily be installed and replaced if necessary, by feeding a new coil spring 20 into the groove formation 22. The charge retaining mechanism 10 is relatively

inexpensive and the groove formation 22 is easy to manufacture compared to the prior art.

The charge retaining mechanism 10 according to the invention is further not particularly sensitive to accumulation of dirt and grime. It further provides a high level of reliability without any significant changes in chamber volume.

The applicant has found that the groove formation 22 can be conveniently manufactured by using an articulated ball head drill (not shown). The ball head of the drill is gradually cut into the inner surface of the barrel 16 until a desired depth is reached. Thereafter the groove formation 22 is cut at a constant depth partially along the circumference of the chamber, after which the groove 22 is gradually cut out of said surface. No heavy-duty lathe is therefore required to cut the groove 22 and the integrity of the barrel 16 is retained during the manufacturing process.

It will be appreciated that variations in detail are possible with a charge retaining mechanism, a gun and a barrel for a gun, both provided with such a mechanism according to the invention without departing from the scope of the appended cliams.

In accordance with an alternative embodiment of the invention, which is not shown, the groove formation is in the form of an open U-shaped groove. With the open U-shaped groove, a relatively larger retainer ring is fed into the retainer mechanism spring, all of which is then inserted into the open U-shaped groove and left to radially expand into and lock in the groove.